Device to Device (D2D) communication refers to direct communication between user equipments, where the adjacent user equipments can transmit data over a direct link in a short-distance range, without a central node (i.e., an eNB) to forward the data.
The Long Term Evolution (LTE) D2D technology refers to D2D discovery and communication processes, controlled by an LTE network, operating in an LTE licensed frequency band. The LTE technology will evolve from the pure wireless mobile cellular communication technology toward a “universal connectivity technology” due to the introduction of the LTE D2D feature.
The LTE D2D technology includes two aspects of a D2D discovery and D2D communication, where the D2D discovery refers to that one D2D user equipment discovers another D2D UE nearby. The discovery between the D2D user equipments is realized using a discovery signal, the discovery signal includes two components of a discovery sequence and a discovery message, where the discovery message can carry some identification information, e.g., device information, application information, a service type, etc., and the discovery user equipment (i.e., the user equipment receiving the discovery signal) identifies the discovered user equipment (i.e., the user equipment transmitting the discovery signal) using such information. The discovery message in the discovery signal is carried over a discovery resource, where a full discovery message can be transmitted over a discovery resource which is generally a physical resource including Physical Resource Blocks (PRBs).
In the D2D discovery process, the D2D user equipment needs to know both a receive resource region in which the discovery signal of the other D2D user equipment is received, and a transmit resource region in which the discovery signal of itself is transmitted, but the D2D user equipment may not transmit and receive the discovery signals concurrently in a sub-frame due to a hardware constraint. In general, discovery resources of the system include a set of sub-frames or a set of PRBs, and the periodicity at which the set of sub-frames or the set of PRBs occurs, where the periodicity refers to a discovery periodicity of the system, as illustrated in FIG. 1. A discovery periodicity of the system may include several sub-frames, each of which includes several PRBs, and generally these sub-frames or PRBs in the coverage area of the network are consecutive uplink or downlink cellular resources (e.g., consecutive uplink sub-frames). The discovery resources are generally configured by the eNB in the coverage area of the network, and are predefined, or are configured by a cluster head beyond the coverage area of the network.
In each discovery periodicity, D2D user equipment may detect the discovery signal of the other D2D user equipments in sub-frame(s) in which no discovery signal is transmitted. Also in each discovery periodicity, the D2D user equipment may transmit a discovery message over a discovery resource, or may transmit a number of same or different discovery messages over a number of discovery resources. A discovery sequence and a discovery message included in a discovery signal may be transmitted over the same discovery resource, or may be transmitted over different discovery resources, but generally the discovery sequence is transmitted together with the discovery message in a discover periodicity. If there are a plurality of discovery sequences, then the sequences will be detected respectively at the receiver to determine the currently used discovery sequence.
In the prior art, the user equipment can not determine the number of discovery resources for the transmitter, and consequently can not detect for the number of discovery resources, thus resulting a potential loss of performance due to a mismatching number of discovery resources; and if the user equipment detects blindly for all the possible numbers of discovery resources, then the complexity of detection may be increased.